Apparatus for inspecting deformation of pipes

ABSTRACT

An apparatus is provided for measuring deformation of a surface of a pipe. The apparatus has a central portion to which a detector section is mounted. At each side, guides are connected to the housing via arms. The housing has a platform below which an inverted U-shaped section is provided, with the platform forming the base of the U. At the rear of this section a wheel is rotatably mounted on an axle. Forward of this, and also within the U-shaped section is mounted a further U-shaped section. This is pivotally mounted at its rear end by means of a pin such that its forward end is free to move vertically. The forward end has mounted within it a further wheel on an axle. Projecting upwards from the second U-shaped section is a rod which passes through a hole in platform. Around the lower portion of the rod is provided a spring which biases the detector downwards and away from the platform. The rod moves vertically with the wheel as it passes over bumps in the pipe. The rod is connected to a potentiometer which varies an output voltage. By correlating the variations in the output voltage with the distance moved by the detector, deformations in the pipe may be mapped.

The present invention provides an apparatus for measuring deformation ofpipes and tubes. The apparatus is particularly useful in the field ofchemical process technology where deformation may be caused by unevenheating of pipes and tubes. The invention also provides a method ofmeasuring deformation of pipes and tubes.

In a thermal cracker unit where heat is used to convert saturatedhydrocarbons into unsaturated hydrocarbons, the reaction mixture isgenerally passed through a furnace in metallic reactor tubes. Crackerunits of this type are used in the process industry in order to providea feedstock of unsaturated hydrocarbon for polymer production and otherapplications.

In order to heat the hydrocarbon reaction mixture in the reaction tubesof the cracker unit, a furnace is generally provided in a chambercontaining a large number of cracker tubes which run parallel to oneanother through the chamber e.g. the pipes may run vertically from floorto ceiling of the chamber. However, the positioning of the furnaceburners relative to the pipes has a tendency to cause hot spots invarious parts of the chamber, and as a result the pipes are subject totemperature differentials. In particular, one side of the pipe i.e. theside closest to the heat source may be subject to higher temperaturesthan the other side, and this leads to a problem with circumferentialcreep i.e. deformation of the pipe around its circumference.

The working lifetime of the reaction tubes is shortened by thisphenomenon, and hence the tubes need to be inspected regularly andreplaced when they become deformed. Indeed, if circumferential creep isnot detected in time and replacement tubes are inserted before the tubesfail, the cracker unit may have to be shut down immediately resulting inlost production time. At worst, this problem presents a serious safetyrisk.

Regular inspections of the cracker tubes are carried out when thecracker unit is shut down for routine maintenance and repair. Howeverthe existing methods of measuring the deformation of cracker tubes aretime consuming and inefficient. Visual inspection and manual measurementof pipe diameter/circumference is often inconvenient because the pipesare close to one another, impeding access to the pipes. Furthermore,scaffolding may be necessary in large chambers in order to reach the toppart of the pipes.

Japanese Patent Application No. 08063873 of Japan Energy discloses anapparatus for inspecting pipelines by using a radiation source that ismoved along the pipes to detect corrosion. This apparatus is howeverdesigned to detect corrosion in pipes, rather than circumferentialdeformation. Furthermore, the method was developed to enable inspectionof pipes without removing a heat insulation layer around the pipe. Thisrenders the apparatus unnecessarily complex for use in cracker units inwhich the pipes are not insulated.

Japanese Patent Application No. 11-211700 discloses an apparatus thatuses ultrasound to detect creep damage in pipes by determining themaximum roughness of the pipe. This it does by transmitting a sound waveinto the pipe such that it passes through the pipe to acircumferentially offset receiving probe. A further probe detects theechoes of reflected waves. However this apparatus is disadvantageousbecause as well as requiring a source of ultrasound and detector probes,comparatively complex calibration and analysis of the output data isrequired.

It will therefore be seen that the prior art does not provide acost-effective and efficient way to measure deformation in pipes such asthose found in petroleum crackers.

Viewed from one aspect, the invention provides an apparatus formeasuring deformation of a surface of a pipe comprising a detectorcapable of directly detecting changes in the radius of a pipe andguide(s) for guiding the detector along the pipe in a direction parallelto the longitudinal axis of the pipe, whereby an output related to thedeformation of the pipe surface is derived from the output of thedetector.

Thus, the apparatus may be guided along a pipe which is being testedsuch that it directly measures changes in the radius of the pipe such asbulges caused by circumferential creep. The apparatus typically doesthis by the detector being arranged to measure the distance between aregion of the pipe adjacent the detector and a part of the apparatus.

Although various sensing devices may be used, such as laser-basedoptical distance sensors, sonic sensors, etc., it is preferred that thedetector is arranged to be placed in contact with the surface of thepipe and is moveable in the radial direction of the pipe. In this way,the deformation of the pipe surface may be determined from thedisplacement of the detector.

Such a measurement apparatus of the invention is ideally suited tomeasure the deformation of a pipe, especially cracker tubes, because itis mechanically simple and easy to operate. It is not expensive tomanufacture and because of its simplicity it is easy to maintain.

Viewed from another aspect there is provided an apparatus for measuringdeformation of a surface of a pipe comprising:

-   -   (i) detector means capable of detecting changes in the radius of        a pipe when placed in contact with the surface of the pipe said        detector means being moveable in the radial direction of the        pipe at the point of contact    -   (ii) a guide means capable of guiding the detector means along        the surface of the pipe in a direction parallel with the        longitudinal axis of the pipe, and    -   (iii) measurement means capable of measuring the radial        displacement of the detector means whereby to produce an output        related to the deformation of the pipe surface.

When the apparatus is in use, the moveable detector is contacted withthe pipe and moved along its surface so that it moves over any bulges,bumps and recesses in the surface of the pipe. As the detector moves inthe radial direction of the pipe, it remains in contact with the pipesurface as the pipe radius changes due to deformation.

The displacement of the detector means is directly related to the radiusof the pipe at the point of contact, and thus the output from themeasurement means gives a qualitative, semi-quantitative or quantitativeindication of the circumferential deformation of the pipe at the pointof contact.

The part of the detector that contacts the pipe may take any suitableform that allows it to maintain contact with the pipe surface whilst itmoves over the surface along the pipe. Thus, it may be a smooth surface,possibly provided with a bearing surface of, for example, nylon or alubricated contact surface. However, the detector is preferably in theform of a rotatable member such as a wheel or roller which is able torotate freely so that it rolls smoothly over the surface of the pipe.This reduces noise and cuts down on wear to the device and the pipe.

A further advantage of using a rotatable member is that it may be usedto determine the total distance travelled by the detector in order tocorrelate output, concerning the pipe's condition with position. Thus,the number of rotations of the member may be counted. Other rotatablemembers provided on the device may additionally or alternatively be usedfor this purpose.

As well as guiding the detector along the pipe, the guide(s) may assistin securing the apparatus firmly in position against the pipe. This ispreferably achieved by providing the guide(s) with magnet(s) arranged tohold the apparatus in position against a steel pipe.

In order for the detector to be moveable in the radial direction of thepipe, the detector may conveniently be connected to the guide(s) in sucha way that the detector is able to move in the radial direction of thepipe relative to the guide(s), whereas the guide(s) do not move in theradial direction of the pipe. For example, the detector may be attachedto the apparatus by means of a pivoted arm, spring or other device whichallows it to move in the direction required, i.e. radially from thecentre of the pipe, when in use.

The guide(s) are provided in order to guide the detector longitudinallyalong the pipe. Thus, they maintain the course of the detector along itspath, over the surface of the pipe without deviating laterally acrossthe surface of the pipe, i.e. to keep the detector travelling parallelto the longitudinal axis of the pipe. In a preferred embodiment theguide(s) comprise two or more rotatable members such as wheels orrollers that are capable of maintaining contact with the surface of thepipe as the measurement apparatus is moved along the pipe. These membersmay be similar to the rotatable member discussed above that may be usedin the detector.

Preferably, the rotatable members of the guides are connected to thedetector means such that they are positioned either side of the detectorand along an imaginary arc having approximately the same radius as thepipe under test. In this way, when the apparatus is in use, the detectorand the guides are both in contact with the surface of the pipe atdifferent points around its circumference. It is particularly preferredthat at least two of the rotatable members in the guide means are spacedapart from one another and from the detector such that the distancebetween the detector and each said rotatable members is smaller than theradius of the arc (and hence smaller than the radius of the pipe undertest).

Where the guide means comprises two or more rotatable members asdescribed above, the rotatable member of the detector may be movablymounted on a housing or platform with each guide member mounted on anarm extending laterally therefrom.

As explained above, the guide means is primarily required in order toguide the detector means along the desired path on the pipe. However,the guide means may also provide other useful functions. Thus in apreferred embodiment, the distance travelled by the guide may bemeasured, for example by counting the revolutions of a rotatable member,so that the position of the detector means may be found.

In addition, the guides provide a useful location in which to mountother types of sensing apparatus such that more than one kind ofmeasurement may be made at the same time.

Of course if the position of the detector means is known at any givenpoint along the pipe, the nature of the deformation of the pipe at eachpoint on the pipe can be easily monitored. The shape and size of bulges,bumps and recesses in the pipe at any given point can be mapped in thisway. As well as providing direct information about the condition of thepipe under test, such information is extremely useful in building up apicture of the heat distribution inside a furnace when it is inoperation. This information is particularly useful to identify hot spotswithin the furnace chamber and it may be possible to make changes to thechamber design to prevent the problem from reoccurring.

There are a number of ways in which to measure the displacement of thedetector means relative to the centre of the pipe under test. A simpleand effective way is to use a linear potentiometer arranged to provide avarying output voltage in proportion to the displacement. This may beplotted against linear distance travelled along the pipe.

Although the apparatus of the invention can be moved manually along thepipe it is preferred that the apparatus further comprises transportingmeans to transport the detector means along the pipe. Such means couldtake any suitable form such as a device which can be positioned at oneend of the pipe with an extending arm which moves the measurementapparatus in a straight path along the pipe. Many suitable mechanismsare known in the art that can achieve this.

It will be appreciated that the invention extends to a correspondingmethod of measuring deformation of a pipe. Thus, viewed from anotheraspect, the invention provides a method of measuring the deformation ofsurface of a pipe using the apparatus of the invention.

Certain embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings:

FIG. 1 is an end view of a measurement apparatus in accordance with apreferred embodiment of the invention in use on a section of pipe;

FIG. 2 is a sectional view along the line A-A of the measurementapparatus of FIG. 1;

FIG. 3 is a sectional view along the line B-B of the measurementapparatus of FIG. 1; and

FIGS. 4 and 5 are schematic views of the measurement apparatus of FIG. 1in use on normal and deformed sections of pipe.

With reference first to FIG. 1, the apparatus 1 is formed with a centralportion 2 to which the detector section 3 is mounted. At each side,guides 4 are connected to the housing via arms 5.

As may also be seen from FIG. 2, the housing has a platform 6 belowwhich an inverted U-shaped section 7 is provided, with the platformforming the base of the U. At the rear of this section a wheel isrotatably mounted on an axle 9.

Forward of this, and also within the U-shaped section is mounted afurther U-shaped section 10. This is pivotally mounted at its rear endby means of a pin 11 such that its forward end is free to movevertically (in the sense of the figures). That forward end has mountedwithin it a further wheel 12 on an axle 13.

These components together form a detector as will be discussed below.

Projecting upwards from second U-shaped section 10 is a rod 14 whichpasses through a hole 15 in platform 16. Around the lower portion of therod is provided a spring 16 which biases the detector downwards and awayfrom the platform.

The upper end of the rod 14 extends into an enclosure which is supportedabove the platform by supports 17. Within the enclosure is provided alinear potentiometer and associated components. Vertical movement of therod 14 causes the potentiometer to change its resistance such that, whenan external voltage is applied, an output voltage is provided inproportion to the movement of the rod. (The electrical components arenot shown for reasons of clarity.)

As may be seen from FIG. 3, the guides 4. (which are similar to eachother) comprise inverted U-shaped sections 18 mounted on the distal endsof arms 5. At the forward end of each is mounted a wheel 19 on an axle20. In addition, behind each wheel is located a permanent magnet 21(these are omitted from FIG. 1 for clarity).

In operation the apparatus is located on the outside of the pipe undertest 22, as shown in FIGS. 1 and 2, such that all four wheels makecontact with the surface of the pipe. Wheels 8 and 19 together form atripod arrangement and wheel 12 moves upwards against the bias force ofthe spring 16. The attractive force of the magnets 21 serve to hold theapparatus firmly in place against the pipe 22, despite the force ofspring 16.

The guide wheels 19 and wheel 8 have parallel axes so they constrain theapparatus to move in a straight line along the pipe and parallel to itsaxis. It may be moved manually, or by means of an external driver onwhich it is mounted (not shown). As the apparatus moves, wheel 12 of thedetector will move to follow the contours of the pipe—upwards for abulge, downwards for a recess. As it moves, it causes a correspondingmovement of rod 14 which in turn varies the resistance of thepotentiometer, as discussed above. This in turn provides a variableoutput voltage representative of the contours of the pipe.

FIGS. 4 and 5 illustrate schematically the effect of a bulge in a pipeon the detector wheel 12. In FIG. 4 the pipe is level so wheel 12,mounted on section 3 is in a low position. In FIG. 5 a bump isencountered which causes wheel 12 to be pushed up, causing section 3 topivot against spring 12.

By comparing the output voltage with the corresponding position of theapparatus, the pipe may be mapped. This may be automated if, as in amodified embodiment (not illustrated), a device is provided to count therevolutions of wheel 8. This device takes the form of a reed switch thatmay be closed by a small magnet on wheel 8 as the wheel reaches itsuppermost position. By using the reed switch to interrupt a circuit, apulse is provided for every rotation of wheel 18. A pulse counter thenprovides a measure of the distance travelled. The output from thepotentiometer and from the counter is then fed to a computer where aplot of voltage (i.e. profile) versus pulses (i.e. distance along pipe)may be produced. This may, of course be calibrated to give readings inmillimetres and metres respectively.

1. An apparatus for measuring deformation of a surface of a pipecomprising a detector capable of directly detecting changes in theradius of a pipe and a plurality of guides for guiding the detectoralong the pipe in a direction parallel to the longitudinal axis of thepipe, the guides comprising rotatable members spaced apart from thedetector and arranged to contact a surface of the pipe when the detectoris in contact with the pipe, wherein a said guide is provided on eachside of the detector, the rotatable members of the guides and thedetector being positioned substantially along an arc, and the distancebetween each said rotatable member of the guide and the detector beingsmaller than. the radius of the arc, whereby an output related to thedeformation of the pipe surface is derived from the output of thedetector.
 2. An apparatus as claimed in claim 1, wherein the detector isarranged to measure the distance between a region of the pipe adjacentthe detector and a part of the apparatus.
 3. An apparatus as claimed inclaim 2, wherein the detector is arranged to be placed in contact withthe surface of the pipe and is moveable in the radial direction of thepipe such that the deformation of the pipe surface may be determinedfrom the displacement of the detector.
 4. An apparatus as claimed inclaim 1, wherein the guide(s) comprise magnet(s) arranged to hold theapparatus in position against a steel pipe.
 5. An apparatus as claimedin claim 1, wherein the detector comprises a rotatable member that isarranged to roll over the surface of the pipe.
 6. An apparatus asclaimed in claim 5, wherein the rotatable member of the detector ismovably mounted cn a housing and each guide member is mounted on an armextending laterally from the housing.
 7. An apparatus as claimed inclaim 5 comprising measurement means for measuring the displacement ofthe rotatable member of the detector in relation to the housing.
 8. Anapparatus as claimed in claim 1 wherein said apparatus further comprisestransporting is means to transport the detector means along the pipe. 9.An apparatus as claimed in claim 1, arranged to measure the distancetraveled by the apparatus along the pipe.
 10. An apparatus as claimed inclaim 9, wherein the distance traveled is determined by measuring thenumber of rotations of a rotatable member engaged with the pipe.
 11. Anapparatus for detecting deformation of a surface of a pipe comprising:(i) a detector capable of detecting changes in the radius of a pipe whenplaced in contact with the surface of the pipe, said detector meansbeing moveable in the radial direction of the pipe at the point ofcontact; (ii) a guide assembly capable of guiding the detector along thesurface of the pipe in a direction parallel with the longitudinal axisof the pipe, wherein the guide assembly comprises rotatable membersprovided on each side of the detector being positioned substantiallyalong an arc, the distance between each said rotatable member of theguide and the detector being smaller than radius of the arc; and (iii)measurement means capable of measuring the radial displacement of thedetector, whereby to produce an output related to the deformation of thepipe surface.
 12. A method of measuring the deformation of surface of apipe using the apparatus as claimed in claim 1.